xpcom/base/Logging.h
author Andreea Pavel <apavel@mozilla.com>
Wed, 18 Sep 2019 13:53:34 +0300
changeset 493713 a3a081ae714f1123bdc23c9d9ef53dfaa783a8de
parent 489621 280a814cd054ff6f61f34e0f578dc9fa1d15fa86
permissions -rw-r--r--
Backed out 9 changesets (bug 1578661) for lints failure at ServoCSSPropList.py a=backout Backed out changeset d16463e5698c (bug 1578661) Backed out changeset c6d64ac858ba (bug 1578661) Backed out changeset db306f1467f7 (bug 1578661) Backed out changeset 273535aab82d (bug 1578661) Backed out changeset f643262a8c25 (bug 1578661) Backed out changeset b0db409ada96 (bug 1578661) Backed out changeset dc96d13728e0 (bug 1578661) Backed out changeset 11e1e8f0a1b7 (bug 1578661) Backed out changeset 6dd7a0d914d9 (bug 1578661)

/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
/* vim: set ts=8 sts=2 et sw=2 tw=80: */
/* This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */

#ifndef mozilla_logging_h
#define mozilla_logging_h

#include <string.h>
#include <stdarg.h>

#include "mozilla/Assertions.h"
#include "mozilla/Atomics.h"
#include "mozilla/Attributes.h"
#include "mozilla/Likely.h"

// We normally have logging enabled everywhere, but measurements showed that
// having logging enabled on Android is quite expensive (hundreds of kilobytes
// for both the format strings for logging and the code to perform all the
// logging calls).  Because retrieving logs from a mobile device is
// comparatively more difficult for Android than it is for desktop and because
// desktop machines tend to be less space/bandwidth-constrained than Android
// devices, we've chosen to leave logging enabled on desktop, but disabled on
// Android.  Given that logging can still be useful for development purposes,
// however, we leave logging enabled on Android developer builds.
#if !defined(ANDROID) || !defined(RELEASE_OR_BETA)
#  define MOZ_LOGGING_ENABLED 1
#else
#  define MOZ_LOGGING_ENABLED 0
#endif

// The mandatory extension we add to log files.  Note that rotate will append
// the file piece number still at the end.
#define MOZ_LOG_FILE_EXTENSION ".moz_log"

namespace mozilla {

// While not a 100% mapping to PR_LOG's numeric values, mozilla::LogLevel does
// maintain a direct mapping for the Disabled, Debug and Verbose levels.
//
// Mappings of LogLevel to PR_LOG's numeric values:
//
//   +---------+------------------+-----------------+
//   | Numeric | NSPR Logging     | Mozilla Logging |
//   +---------+------------------+-----------------+
//   |       0 | PR_LOG_NONE      | Disabled        |
//   |       1 | PR_LOG_ALWAYS    | Error           |
//   |       2 | PR_LOG_ERROR     | Warning         |
//   |       3 | PR_LOG_WARNING   | Info            |
//   |       4 | PR_LOG_DEBUG     | Debug           |
//   |       5 | PR_LOG_DEBUG + 1 | Verbose         |
//   +---------+------------------+-----------------+
//
enum class LogLevel {
  Disabled = 0,
  Error,
  Warning,
  Info,
  Debug,
  Verbose,
};

/**
 * Safely converts an integer into a valid LogLevel.
 */
LogLevel ToLogLevel(int32_t aLevel);

class LogModule {
 public:
  ~LogModule() { ::free(mName); }

  /**
   * Retrieves the module with the given name. If it does not already exist
   * it will be created.
   *
   * @param aName The name of the module.
   * @return A log module for the given name. This may be shared.
   */
  static LogModule* Get(const char* aName);

  /**
   * Logging processes -MOZ_LOG and -MOZ_LOG_FILE command line arguments
   * to override or set modules and the file as if passed through MOZ_LOG
   * and MOZ_LOG_FILE env vars.  It's fine to pass (0, nullptr) if args
   * are not accessible in the caller's context, it will just do nothing.
   * Note that the args take effect (are processed) only when this function
   * is called the first time.
   */
  static void Init(int argc, char* argv[]);

  /**
   * Sets the log file to the given filename.
   */
  static void SetLogFile(const char* aFilename);

  /**
   * @param aBuffer - pointer to a buffer
   * @param aLength - the length of the buffer
   *
   * @return the actual length of the filepath.
   */
  static uint32_t GetLogFile(char* aBuffer, size_t aLength);

  /**
   * @param aAddTimestamp If we should log a time stamp with every message.
   */
  static void SetAddTimestamp(bool aAddTimestamp);

  /**
   * @param aIsSync If we should flush the file after every logged message.
   */
  static void SetIsSync(bool aIsSync);

  /**
   * Indicates whether or not the given log level is enabled.
   */
  bool ShouldLog(LogLevel aLevel) const { return mLevel >= aLevel; }

  /**
   * Retrieves the log module's current level.
   */
  LogLevel Level() const { return mLevel; }

  /**
   * Sets the log module's level.
   */
  void SetLevel(LogLevel level) { mLevel = level; }

  /**
   * Print a log message for this module.
   */
  void Printv(LogLevel aLevel, const char* aFmt, va_list aArgs) const
      MOZ_FORMAT_PRINTF(3, 0);

  /**
   * Retrieves the module name.
   */
  const char* Name() const { return mName; }

 private:
  friend class LogModuleManager;

  explicit LogModule(const char* aName, LogLevel aLevel)
      : mName(strdup(aName)), mLevel(aLevel) {}

  LogModule(LogModule&) = delete;
  LogModule& operator=(const LogModule&) = delete;

  char* mName;

  // Logging atomics and other state are not preserved by web replay, as they
  // may be accessed during the GC and other areas where recorded events are
  // not allowed.
  Atomic<LogLevel, Relaxed, recordreplay::Behavior::DontPreserve> mLevel;
};

/**
 * Helper class that lazy loads the given log module. This is safe to use for
 * declaring static references to log modules and can be used as a replacement
 * for accessing a LogModule directly.
 *
 * Example usage:
 *   static LazyLogModule sLayoutLog("layout");
 *
 *   void Foo() {
 *     MOZ_LOG(sLayoutLog, LogLevel::Verbose, ("Entering foo"));
 *   }
 */
class LazyLogModule final {
 public:
  explicit constexpr LazyLogModule(const char* aLogName)
      : mLogName(aLogName), mLog(nullptr) {}

  MOZ_NEVER_INLINE_DEBUG operator LogModule*() {
    // NB: The use of an atomic makes the reading and assignment of mLog
    //     thread-safe. There is a small chance that mLog will be set more
    //     than once, but that's okay as it will be set to the same LogModule
    //     instance each time. Also note LogModule::Get is thread-safe.
    LogModule* tmp = mLog;
    if (MOZ_UNLIKELY(!tmp)) {
      tmp = LogModule::Get(mLogName);
      mLog = tmp;
    }

    return tmp;
  }

 private:
  const char* const mLogName;

  // As for LogModule::mLevel, don't preserve behavior for this atomic when
  // recording/replaying.
  Atomic<LogModule*, ReleaseAcquire, recordreplay::Behavior::DontPreserve> mLog;
};

namespace detail {

inline bool log_test(const LogModule* module, LogLevel level) {
  MOZ_ASSERT(level != LogLevel::Disabled);
  return module && module->ShouldLog(level);
}

void log_print(const LogModule* aModule, LogLevel aLevel, const char* aFmt, ...)
    MOZ_FORMAT_PRINTF(3, 4);
}  // namespace detail

}  // namespace mozilla

// Helper macro used convert MOZ_LOG's third parameter, |_args|, from a
// parenthesized form to a varargs form. For example:
//   ("%s", "a message") => "%s", "a message"
#define MOZ_LOG_EXPAND_ARGS(...) __VA_ARGS__

#if MOZ_LOGGING_ENABLED
#  define MOZ_LOG_TEST(_module, _level) \
    MOZ_UNLIKELY(mozilla::detail::log_test(_module, _level))
#else
// Define away MOZ_LOG_TEST here so the compiler will fold away entire
// logging blocks via dead code elimination, e.g.:
//
//   if (MOZ_LOG_TEST(...)) {
//     ...compute things to log and log them...
//   }
#  define MOZ_LOG_TEST(_module, _level) false
#endif

// The natural definition of the MOZ_LOG macro would expand to:
//
//   do {
//     if (MOZ_LOG_TEST(_module, _level)) {
//       mozilla::detail::log_print(_module, ...);
//     }
//   } while (0)
//
// However, since _module is a LazyLogModule, and we need to call
// LazyLogModule::operator() to get a LogModule* for the MOZ_LOG_TEST
// macro and for the logging call, we'll wind up doing *two* calls, one
// for each, rather than a single call.  The compiler is not able to
// fold the two calls into one, and the extra call can have a
// significant effect on code size.  (Making LazyLogModule::operator() a
// `const` function does not have any effect.)
//
// Therefore, we will have to make a single call ourselves.  But again,
// the natural definition:
//
//   do {
//     ::mozilla::LogModule* real_module = _module;
//     if (MOZ_LOG_TEST(real_module, _level)) {
//       mozilla::detail::log_print(real_module, ...);
//     }
//   } while (0)
//
// also has a problem: if logging is disabled, then we will call
// LazyLogModule::operator() unnecessarily, and the compiler will not be
// able to optimize away the call as dead code.  We would like to avoid
// such a scenario, as the whole point of disabling logging is for the
// logging statements to not generate any code.
//
// Therefore, we need different definitions of MOZ_LOG, depending on
// whether logging is enabled or not.  (We need an actual definition of
// MOZ_LOG even when logging is disabled to ensure the compiler sees that
// variables only used during logging code are actually used, even if the
// code will never be executed.)  Hence, the following code.
#if MOZ_LOGGING_ENABLED
#  define MOZ_LOG(_module, _level, _args)                      \
    do {                                                       \
      const ::mozilla::LogModule* moz_real_module = _module;   \
      if (MOZ_LOG_TEST(moz_real_module, _level)) {             \
        mozilla::detail::log_print(moz_real_module, _level,    \
                                   MOZ_LOG_EXPAND_ARGS _args); \
      }                                                        \
    } while (0)
#else
#  define MOZ_LOG(_module, _level, _args)                      \
    do {                                                       \
      if (MOZ_LOG_TEST(_module, _level)) {                     \
        mozilla::detail::log_print(_module, _level,            \
                                   MOZ_LOG_EXPAND_ARGS _args); \
      }                                                        \
    } while (0)
#endif

// This #define is a Logging.h-only knob!  Don't encourage people to get fancy
// with their log definitions by exporting it outside of Logging.h.
#undef MOZ_LOGGING_ENABLED

#endif  // mozilla_logging_h